Because of excellent properties in specific strength, specific modulus of elasticity, fatigue strength and resistance to abrasive wear, the ceramic-reinforced Al alloy composite material, a product formed by integrally compounding a lightweight metal Al alloy with ceramics, has been drawing keen attention as a material for structural members of aerospace crafts, automobiles and office automation appliances or as a material for sports equipments.
The ceramic-reinforced Al alloy composite material is produced by a process of mixing Al alloy powder with reinforcing ceramic whisker or particles, preforming the powder mixture by hot pressing or hot isostatic pressing (HIP) and sintering the resulting shape or billet under pressure. In this instance, the properties of the product composite material are largely influenced by the dispersibility of the ceramic in the powder mixture, and therefore it is an important technical point to mix Al alloy powder uniformly with ceramic. The technology in this regard is important especially in a case where the ceramic is in the form of whiskers which easily get entangled. In an attempt to overcome this problem, Applicants proposed in their Japanese Laid-Open Patent Applications 62-89801 and 60-251922 a method of mixing the two materials uniformly by applying ultrasonic vibrations to whisker in an organic solvent, adding Al alloy powder with stirring, filtering by suction the resulting slurry of powder mixture, and removing the organic solvent by vacuum-drying the cake.
As the matrix, an Mg-containing Al alloy with age-strengthening property is generally used.
Although the above-described mixing means has made it possible to produce composite material of uniform properties, the art has not yet arrived at a stage where it can fully respond to the demands for further improvements in strength and modulus of elasticity.